Abstract: A method of measuring the in-situ Total Gas content of an unconventional reservoir rock, the method including: drilling a borehole through a measurement interval in the reservoir to generate an annular volume of drilling mud that includes cuttings and gas, the annular volume having a leading edge and a trailing edge; diverting the leading edge of the annular volume such that all of the annular volume is captured in a degassing storage system without being exposed to atmosphere; discontinuing the diversion of the annular volume when the trailing edge of the annular volume has been captured in the degassing storage system; measuring the gas volume in the degassing storage system to determine the amount of gas per annular volume; and calculating the in-situ Total Gas content of the reservoir with reference to the amount of gas and cuttings per annular volume.